Antenna Project

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I am creating a ham radio antenna mast out of a 21' piece of schedule 80, 2" (ID) pipe - 2 3/8 OD.  3' are in concrete in the ground and I have a custom bracket bolting the pipe to the house at 8' above ground - leaving about 10' up in the air.  The 25 pound, 30' antenna will mount at the top of the mast.My question:  considering the wind loads on the pipe mast, will welding the bracket to the pipe mast at 8' weaken the pipe in any way?The bracket is 3/16' angle (2x1.5), which is cut to touch the pipe all the way around.Thank you.
Reply:I would probably have something in a sideways V configuration. The portion you have now attached to your house, then another attachment point from there to the top of your mast.  Like this: <John -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:Something a little like this: Attached ImagesJohn -  fabricator extraordinaire, car nut!-  bleeding Miller blue! http://www.weldfabzone.com
Reply:I've been in ham for years and did the following quite a few times:I use the same pipe that you mention. At 40', sink it in the ground 3' and use a 25# bag of concrete. The closer you get the mast to the house, the better. I tie 2 points to the structure. I use a 2.5" exhaust clamp with the stamped steel portion welded to the brace that ties to the structure. The "U" clamp mounts the brace to the mast. I use 5/16" toggle bolts to mount the brace to the house.I've used 40/20/15/10 meter beams and the mast survives 80 MPH winds at 35' mounted to a 1.5 storie house.
Reply:It all hinges around the strength of that house bracket. I don' think the strength of the pipe above ground is at question as much as 17 feet of leverage provided during wind/loading conditions. If the bracket is decent enough it all starts over right there at that point and with only ten feet of of schedule 80 sticking up you should be able to do trapeze acts up there.If it's some little flimsy thing then any severe wind loading on a beam antennae is going to eventually have it's way with the bracket. As far as only 17 feet of schedule 80 pipe sticking out of the ground it wouldn't bother me to go up there. The weakest point would be that where the pipe mates with the concrete. It'll be wobbly as the dickens.  That wobble is what you probably don't want. To stop that you need a hefty bracket.
Reply:Thank you to everyone for your posts.  I will let you know how it turns out on Saturday - when I put the ladder up to the 18' mark to mount the antenna.  The bracket I made is out of 3/16" angle steel (1.5x2").  It is very strong.  I was only worried about the weld joint between the bracket and the pipe, weakening the pipe (does not seem to have weakened it at all).  So far it seems like an ideal solution!  I appreciate everyone taking the time to comment.Thank you.
Reply:A 40 foot post anchored 3 feet deep in -ONE- 25 pound bag worth of concrete!?!Sheesh, my mailbox post has an in-ground base of 200 pounds of concrete!  That's just three 70 pound bags, and the base at ground level is only about 9x12 inches rectangular.Now a lot depends on the bracing and bracketing and guy wires used, but I don't think I'd feel too comfortable with 240 pounds of pipe sticking 40 feet up into the air just sitting in 25 pounds of concrete.  Heck, even a 12" diameter form 3' deep would use 2.4 ft3 of concrete (somewhere between approximately 180 and 350 pounds of concrete depending on the mix used and the density of the aggregrate used).I think you already welded to the Sch. 80 pipe, but you could just use U-bolts around the pipe/mast to attach to a mounting plate and have your braces welded to the mounting plate.Next, angle iron is OK for tension loads but behaves badly in compression or bending.  Once the 'cross' leg starts to bend/buckle, the whole piece bends/buckles.  That said, your heavy pipe and 3/16" 1.5" x 2" angle iron should be pretty strong because of material thickness overkill.Oh, obviously attach the brace to a STRUCTURAL part of the house with some structural attachment(s).  No molly bolts to the drywall or siding or sheathing, attach it to some big framing members with lag bolts or similar.  You might want to sister or double-up or otherwise reinforce whatever you are attaching the brackets to also.Yeah, I believe in design and fabrication overkill.  Do it once and do it right, this way you don't have to go back and fix it and whatever pulled loose.